ADuCM350 FAQ AFE / ADC Measurement Channel

Document created by LiamR Employee on Apr 24, 2014Last modified by LiamR Employee on Aug 28, 2014
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Q: How to calculate current resolution ?

A: Input Current Resolution = 3.6V/2^16 x 1/1.5 x 1/RTIA = 14.6nA (assumption RTIA=2.5k as in diagram below )

 

Picture1.jpg

 

 

 

Q: Can I do a differential measurement using ADC Mux.

A: Yes. Use the P-N channel option. The caveat is that you have AFE pins available to switch the P and N channels out.The excitation buffer and IN-amp should be powered down in the AFE Sequence during the P-N measurement.

 

Differential Measurement P-N.jpg

Q: What are the data update rates ?

A:

  • If using the DFT then a Real and Imaginary component of the impedance is available every 12.8mS.
  • If using PSR filter settling time is 900SPS.
  • Raw ADC data is available at 160KSPS - This is FIXED - no configurability. If other sample rate required the raw data can be averaged in Core.

 

Q: Dynamic Range of ADC ?

A: Typically 95 dB

 

Q: Details on precision specifications ?

A: See ADuCM350 Datasheet.

 

Q: What is the maximum common mode ? ADC input range ? Etc

A: Please refer to the "AFE Signal Swings" section in AFE Excitation Loop chapter of UG-587 and the ADC Measurement section

in ADC Chapter of UG-587.

 

Q: Hoe much current can you sink into load ?

A: Typically 5mA.

 

Q: What is Non-Coherent Sampling ?

A: Example scenarios is where the DAC and ADC are clocked st 160KHz. The images of the excitation frequency can be aliased back into the same FFT bin as the fundamental. By developing a non-choherent excitation signal by changing the DAC update rate you prevent the aliased images from falling inside this fundamental bin.

 

Q: Why should I only use 1/8 to 7/8 of the ADC and DAC available ranges?

A:The rest of the range is used in the autocalibration sequnces to remove offset and gain effects. See No Factory Cal chapter in UG-587.

 

 

Q: I am measuring 1/2VCCMANA through the ADC MUX selector. With a 3V VCCM at pin I am measuring ~2.87 V. Why the disparity ?

A:  To divide down the VCCM signal by 2 a potential divider is used (R1 and R2). These resistors have limited matching capability which allows for an accuracy spec of 1% for all of these general monitoring functions on the ADC Mux.

VCCM.png

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